1. Field of the Invention
The invention relates to a backlight unit using a light emitting diode, and more particularity, to a light emitting diode (LED) backlight unit in which a light guide plate is assembled without a thermosetting adhesive affecting brightness of the LED, and which assures higher radiation efficiency of heat generated from the LED, thereby maintaining high brightness, and significantly enhancing productivity.
2. Description of the Related Art
Development in the electronic device industry also has led to development in various small display devices with less energy consumption rate, and in image devices, computers and telecommunication terminals using such display devices. A liquid crystal display (LCD) emerged in line with this trend and has been highlighted as a display device for monitors and mobile telecommunication terminals.
In general, the LCD fails to generate light voluntarily, which thus necessitates a backlight unit including a light source for generating light and a light guide plate on a rear side of the LCD panel.
The backlight unit generates a white light so that the LCD panel produces an image in almost true-to-life color.
FIG. 1 illustrates a conventional backlight unit 100 using a light emitting diode (LED). The light emitting diode (LED) used in the conventional backlight unit 100 generates light by virtue of luminescence (electroluminescence) arising when voltage is applied to a semiconductor.
The LED is smaller in size and longer in useful life than the conventional light source. Also, the LED as a light source exhibits high energy efficiency and low driving voltage due to direct conversion of electrical energy into optical energy.
Therefore, in the backlight unit 100 with these merits, as shown in FIG. 1, a light source 120, a light guide plate 130, a plurality of diffuser sheets 140 and a plurality of prism sheets 150 are disposed inside a bottom chassis 110 and fixed by a middle chassis 160 and a mold frame 162.
The light source 120 includes a substrate with superior heat radiation properties (MCPCB) 122 and a plurality of light emitting diodes 124. Here, the LEDs 124 are arranged in rows on the substrate 122 and electrically connected to an external power voltage (not illustrated).
The light guide plate 130 is of a flat type and made of a transparent acryl. The light guide plate 130 is linear at one side which is placed adjacent to the light source 120. The light guide plate 130 receives light generated from the LEDs of the light source 120 and diffuses the light through an entire top surface thereof. A reflective film (not illustrated) is fixedly disposed on an underside surface of the light guide plate 130 to induce light only toward the top surface of the light guide plate 130.
The diffuser sheets 140 are structured of a flat sheet type in the same manner as the light guide plate 130, and disposed on the light guide plate 130. The diffuser sheets 140 serve to uniformly diffuse light that propagated through the light guide plate 130.
Further, the prism sheets 150 disposed on the diffuser sheets 140 induce light from the diffuser sheets 140 into a predetermined area (image forming area) of an LCD panel (not illustrated) located thereover.
Meanwhile, as described above, the substrate 122 having a plurality of LEDs 124 disposed thereon is fastened onto a lower chassis 110 via a thermosetting adhesive 112 as shown in FIGS. 2 and 3.
That is, in the conventional backlight unit 100, the light source 112 is fastened onto the lower chassis 110 via the thermosetting adhesive 112 to be fixedly positioned with respect to the light guide plate 130.
Also, in order to prevent the guide light plate 130 from impacting the LEDs 124 of the light source 120, an attachment 114 is disposed at both sides in an inner periphery of the lower chassis 110 thereby to prevent the light guide plate 130 from being pushed toward the LEDs 124.
In consequence, light emitted from the LEDs 124 of the light source 120 is radiated outside through the light guide plate 130 and then the diffuser sheets 140 and the prism sheets 150.
However, in the conventional backlight unit 100, the LEDs 124 of the light source 120 start to radiate heat just when emitting light, thus greatly undermining brightness of the LEDs 124. Accordingly, the LEDs 124, if incapable of radiating heat smoothly after being ignited, is gradually reduced in brightness thereby not attaining desired high brightness.
In order to ensure such heat radiation effects, the LEDs are disposed on the substrate 122 to radiate heat outside effectively. Yet, the thermosetting adhesive 12 through which the substrate 122 is fastened to the lower chassis 110 considerably degrades heat radiation effects.
What is more, the substrate, if warped, can not be spaced adequately from the light guide plate 130 in the warped portion, thereby not achieving desired high brightness.
In addition, during an assembling process, the thermosetting adhesive 112 should be applied on a rear side of the substrate 122. Here, the thermosetting adhesive, if applied in an inappropriate amount, may be smeared on the LEDs 124, resultantly blocking light from the LEDs 124.
Besides, the thermosetting adhesive 112 is applied on the substrate 122 through a very intricate and tedious process, thereby adversely affecting productivity.